Delineation of the mechanisms of tendon gliding resistance within the carpal tunnel

Abstract

Background Forceful, high-velocity, and repetitive manual hand tasks contribute to the onset of carpal tunnel syndrome. This study aimed to isolate and identify mechanisms that contribute to tendon gliding resistance in the carpal tunnel. Methods Eight human cadaver hands (four pairs) were used. Tendon gliding resistance (force, energy, and stiffness) was measured under different conditions: with intact and with divided subsynovial connective tissue, at 2 mm/s and 60 mm/s tendon excursion velocity, and with and without relaxation time before tendon excursion. Results Subsynovial connective tissue stretching substantially contributed to increased gliding resistance force and energy during higher tendon excursion velocities, and subsynovial connective tissue stiffening was observed. Poroelastic properties of the tendon (and possibly the subsynovial connective tissue) also appear to be involved because relaxation time significantly increased gliding resistance force and energy (P<.01), and the difference in energy and force between high- and low-velocity tendon excursions increased with relaxation time (P=.01 and P<.01). Lastly, without relaxation time, no difference in force and energy was observed (P=.06 and P=.60), suggesting contact friction. Interpretation These findings are consistent with the hypothesis that the mechanics of tendon motion within the carpal tunnel are affected by the integrity of the subsynovial connective tissue. While not tested here, in carpal tunnel syndrome this tissue is known to be the fibrotic, thickened, and less-fluid-permeable. An extrapolation of our findings suggests that these changes in the subsynovial connective tissue of carpal tunnel syndrome patients could increase contact friction and carpal tunnel pressure.

Relationships and Mechanisms Between Occupational Risk Factors and Distal Upper Extremity Disorders

“…Tendon frictional work is postulated as a central biomechanical measure in the relationship between workplace risk factors and injury, especially pertaining to tenosynovitis (Moore, Wells, & Ranney, 1991; Tanaka & McGlothlin, 1993). Frictional force is encountered due to shear contact stresses, as well as deformation of the tendons and subsynovial connective tissue (SSCT), a multilayered structure facilitating tendon motion (Filius et al, 2017; Kociolek, Tat, & Keir, 2015). Compared with 11 other biomechanical measures, frictional work was modeled as the most sensitive to changes in workplace exposures (force, repetition, posture) and the best predictor of hand/wrist workplace injuries (Moore et al, 1991).…”

The biomechanics of subsynovial connective tissue in health and its role in carpal tunnel syndrome

“…This model allowed for differentiation between these three different components and their contribution to the total GR was measured at both a low (2 mm/s) as well as a higher (60 mm/s) velocity tendon excursion. The relative SSCT contribution to the GR ranged between 50% to almost a 100% at full physiological excursion and was most clearly present if in the experimental setting the fastest motions without relaxation time were used (Filius et al, 2017). The SSCT influence on the decreasing total GR thus increases when moving the tendon relatively quickly and not allowing for SSCT recovery.…”

PDGFR Signaling Mediates Hyperproliferation and Fibrotic Responses of Subsynovial Connective Tissue Cells in Idiopathic Carpal Tunnel Syndrome

“…The increasing actin stress fiber upregulates mechanosensitivity and the subjected mechanical stress differentiated into activated fibroblast/myofibroblast 45 , 46 . The reduction in stress fibers by activation of AMPK may attenuate mechanosensitivity in SSCT cells, suggesting that metformin may reduce CTS progression by mechanical stress, which is caused by friction force on SSCT during wrist and finger motion 47 , 48 .…”